Lifting jack

ABSTRACT

The lifting jack described herein incorporates a handle, a rack bar, a holding pawl for engaging the rack bar, coordinated linkage members, a wheel pawl and a toothed wheel functioning between the handle and the rack bar, a contoured spring interconnecting the pawls, and a manually-actuated selector lever for engaging or freeing the spring, the combination responding to the actuation of the handle to raise and lower an automobile in a highly efficient manner.

United States Patent [1 1 Valade [54] LIFTING JACK [4 1 Jan. 9, 1973Joyce ..254/95 Hunz ..254/l09 Primary Examiner-Othell M. SimpsonAssistant Examiner-Robert C. Watson Attorney--Warren E. Finken et al.

[57] ABSTRACT The lifting jack described herein incorporates a handle, arack bar, a holding pawl for engaging the rack bar, coordinated linkagemembers, a wheel pawl and a toothed wheel functioning between the handleand the rack bar, a contoured spring interconnecting the pawls, and amanually-actuated selector lever for engaging or freeing the spring, thecombination responding to the actuation of the handle to raise and loweran automobile in a highly efficient manner.

7 Claims, 13 Drawing Figures PATENTEDJM 9 I975 3,709,465

SHEET 2 BF 2 PRIOR ART JACK 7-7 '8 A HANDLE I HORIZONTAL ABOVE BELOWHANDLE TRAVEL (DEGREES) EFFORT (LB) LIFTIING JAtCK This inventionrelates generally to lifting jacks and, more particularly, to liftingjacks of a type suitable for use with automobiles or other vehicles.

The conventional automobile jack includes .a rack bar, a handle, a pairof pawls engaging the rack bar, one for holding and one for lifting,with a spring interconnected therebetween and a selector lever foralternately manually contacting and withdrawing either from a midpointon the spring or from one of the pawls for effectuating the raising andlowering of the automobile.

It is an object of the invention to provide an improved automobile jackwhich incorporates means for increasing the mechanical advantagetherein, resulting in the raising and lowering of an automobile with aminimum of effort having to be exerted on the handle of the jack.

Another object of the invention is to provide an improved automobilejack employing a toothed wheel intermediate the rack bar and a drivingor wheel pawl, the wheel pawl serving to cause the wheel to Walk" up ordown the rack bar as required to cooperate with a holding pawl forraising and lowering an automobile.

A further object of the invention is to provide an improved automobilejack including a housing mounted around a toothed rack bar with a handlepivotally mounted on the housing, a pair of pivotally interconnectedlinkage members pivotally connected between a rotatable end of thehandle and a toothed wheel whose teeth mesh with those on the rack bar.A contoured spring is connected at its ends respectively to a holdingpawl which cooperates with the teeth on the rack bar, and to a wheelpawl which cooperates with the teeth of the wheel. A tab on thereversing lever either abuts against the spring to urge its ends and,hence, the two pawls in particular directions upon movement of thehandle, or is released from the spring to cause its ends to reverse thedirections of their forces and, consequently, the pawls in the oppositedirections upon reverse movement of the handle.

These and other objects and advantages of the invention will becomeapparent when reference is made to the following description andaccompanying drawings, wherein:

FIG. 1 is a fragmentary perspective view showing the application of ajack to an automobile;

FIG. 2 is a side view of an automobile jack embodying the invention;

FIGS. 3, 4, and 6 are fragmentary cross-sectional views taken along theplanes of the lines 33, d-4, and 6-6, respectively, of FIG. 2, andlooking in the direction of the arrows;

FIG. Sis a perspective view ofa portion of FIG. 2;

FIG. 7 is a fragmentary cross-sectional view taken along the plane ofline 7-7 of FIG. 6, and looking in the direction of the arrows;

FIGS. 8-12 are fragmentary views illustrating various operativepositions of the components of the FIG. 2 structure; and

FIG. 13 is a graph illustrating an operational characteristic of theinvention.

Referring now to the drawings in greater detail, FIG. 1 illustrates alifting jack 10 for use on a conventional bumper 12 of an automobile M.The jack 110 includes a stamped metal base 16 which supports an uprighttoothed rack bar 18 having a plurality of teeth 20 formed at spacedintervals thereon. A housing 22, having vertical opening 23 formedtherethrough, is mounted around the toothed bar 18. A handle 24 ispivotally connected to one end thereof by a pivot pin 25 to the housing22 on the toothed side of the bar 18, while a lifting member 26 ispivotally connected by a pivot pin 27 to the opposite side of thehousing 22 for lifting contact with the bumper 12. The lifting member 26is removable inasmuch as the pivot pin 27 is snapped into a notch 28(FIG. 2) of the housing 22, and retained therein by a spring 29. Areversing or selector lever 36]) is pivotally mounted on a pin 31extending into the housing 22, as will be explained.

Referring now to FIGS. 2 and 3, it may be noted that the housing 22includes a holding pawl 32 pivotally mounted at one end on a pivot pin33 secured to the housing 22. A projection 34 is formed on the free endof the holding pawl 32 for cooperation with the notches or slots 35formed on the rack bar 1% by adjacent teeth 20. A tab 36 is formedadjacent the holding pawl 32 by bending aportion ofa side of the housinginwardly, for limiting the rightward movement of the holding pawl 32. Afirst substantially straight link 37 is pivotally connected to a pivotpin 38 mounted on the pivoted end 40 of the handle 22, the end 40consisting of spaced-apart extensions 41 of the handle 24 straddling thelink 37. A boomerang-shaped second link 42, having an arcuateintermediate portion 43, is pivotally connected at one end thereof tothe free end of the first link 37 by means of a pivot pin it, and at itsother end to a pivot pin 46 extending through the center of a toothedwheel 48. The teeth S il of the wheel 48 mesh with the slots 35 on thetoothed rack bar 18.

A driving or wheel pawl 52 is pivotally connected at one end thereof bya pivot pin 54 to the intermediate arcuate portion $3 on the second link42 and has a downwardly extending projection 56 formed on the other endthereof for cooperation with the notches or slots 58 formed betweenadjacent teeth 50 of the wheel 48. An arcuate tab 59 is formed adjacentthe wheel pawl 52 by bending a portion of one side of the housing 22inwardly, as illustrated in FIG. 4, to cam the wheel pawl 52 downwardinto the slots 58 of the wheel 48 as the wheel pawl 52 moves to the leftin FIG. 2.

A contoured resilient member or spring 60 (FIG. 5) has arcuate sections62, 64, and 66 formed thereon, with a straight section 68interconnecting the arcuate sections as and 64, and straight sections 70and 72 interconnected by an intermediate bend 74 extending between thearcuate sections 64 and 66. A straight section 76 extends from thearcuate section 66 substantially parallel to the straight section 72,while a short straight section 78 extends from the arcuate section 62substantially parallel to the straight section 68. Further straightsections 30, 82, and 84 extend substantially at right angles from thestraight sections 78, 80, and 82, respectively. A projection 86 isformed on the end of the straight section 84. A laterally extendingstraight section 82 extends substantially at a right angle from thestraight section 76, substantially parallel to the laterally extendingstraight section 84.

It may be noted in FIG. 3 that the arcuate section 64 of the spring 64Bis positioned around a spacer 90 mounted on the pivot pin 33intermediate the housing 22 and one of a pair of oppositely disposedwashers 92 and 94 adjacent the holding pawl 32, with the straightsection 84 thereof extending through an opening 96 (FIG. 3) formed inthe holding pawl 32. An inwardly extending tab or projection 98 (FIG. 6)formed on the reversing lever 30 extends through a right-angled opening100 (FIG. 7) formed in the housing 22 and is positioned adjacent theupper side of the straight section 70 of the spring 60. The mounting pin31 of the reversing lever 30 also extends through the opening 100,slidably retained therein by rivet heads I02 and MM- adjacent the lever30 and the inner surface of the housing 22, respectively. The straightspring section 88 extends through an opening 106 (FIG. 4) formed in thedriving pawl 52. As illustrated in FIG. 7, the opening H includeshorizontal and vertical camming surfaces 108 and 110, respectively.

OPERATION Raising the Vehicle The reversing lever 30 (FIG. 2) is raisedfrom the A position, FIG. 7, to the B position, the tab 98 being cammedalong the surface MP8 of the opening 100. In the B position, the tab 98has its narrower edge in contact with the upper side of the straightspring section 70, causing the latter to be bowed downwardly.

Referring now to operational FIG. 8, as the handle 24 is lowered, thedriving pawl 52 is moved leftwardly due to the resultant pivoting of therespective straight and boomerang-shaped interconnected linkage members37 and 42 about the pivot pin 46. Leftward movement of the driving pawl52 rotates the toothed wheel 48 in a counterclockwise direction causingthe teeth 50 thereof to walk up the slots 35 of the rack bar 18, therebyraising the vehicle 141. Upward movement of the wheel 48 and housing 22raises the holding pawl 32 upwardly, camming the projection 34 out ofits particular slot 35 in the rack bar 18. The projection 34 is retainedin contact with the next upper tooth and urged into the next upper slot35 by the straight section 84 of the spring 60, the latter exertingrespective leftward and downward forces at the left and right endsthereof by virtue of its being bowed, as described above, at anintermediate point therealong by the tab 98 formed on the reversinglever 34).

Once the projection 34 of the holding pawl 32 enters the next upper slot35 of the rack bar 18, it loads up for the raising of the handle 24. Asthe handle 24 is raised (FIG. 9), the now counterclockwise rotatingpivot pin 38 on the end 40 of the handle 24 causes the arcuateshapedlink 42 to pivot in a clockwise direction about the pivot pin 46,causing the projection 56 of the wheel pawl 52 to be cammed out of itsslot 58 in the toothed wheel 48, over the adjacent tooth 50, into thenext right slot 58 (FIG. 9), as a result of being urged downwardly bythe arcuate section 66 and the straight sections 76 and 88 of the spring60. The wheel or driving pawl 52 is thus ready to rotate the wheel 48another increment upon the next lowering stroke of the handle 24.Lowering the Vehicle The reversing lever 30 is manually actuatedleftwardly from position B" in FIG. 7, the pin 31 being cammeddownwardly along the surface 1110 of the opening 100, causing the tab 38of of the lever 30 to be moved away from the upper surface of thestraight section 70 of the spring 64) to position A of FIG. 7 and asillustrated in FIG. liill. This reverses the forces exerted by therespective straight end sections 84 and 88 of the spring 60, by virtueof the spring 60 no longer being restrained at the straight section 70thereof, the forces at the ends now being generally rightwardly for thearcuate spring section 62 and the straight section 84, and upwardly forthe straight sections 76 and 88.

With the handle 24 in its uppermost position, the load is acting throughthe holding pawl 32 and the spring 60 has pulled the driving pawl 52from its slots 58 in the wheel 48. As the handle 24 is lowered, theclockwise rotation of the pivot pin 38 on the end 40 of the handle 24rotates the respective straight and arcuate-shaped interconnectedlinkages 37 and 42 in a counterclockwise direction. This action movesthe wheel pawl 52 leftwardly (FIG. 10) until the projection end of thepawl 52 abuts against and is projected downwardly by the underside ofthe curved tab 59 into the next left slot 58 (FIG. 10). At the bottom ofthe stroke of the handle 24 (FIG. ii), the projection 56 of the wheelpawl 52 loads up in the right-hand side of the slot 53 of the toothedwheel 48, while the projection 34 of the holding pawl 32 is pulled outof its particular slot 35 by the above-mentioned generally rightwardforce of the straight end section 84 of the spring 60. The wheel 43 isthus in condition to be rotated in a clockwise direction by theprojection 56 and the projection 34 is free to proceed toward the nextlower slot 35 along the rack bar 1%.

As the handle 24 is once again moved upwardly (FIG. 12), the toothedwheel 48 is caused to rotate in a clockwise direction, its teeth 50walking down the notches 35 of the rack bar 118, lowering the vehicle14, the load thereof being felt at the end of the lever arm of thehandle 24, with the projection 56 of the wheel pawl 52 being held inposition in the notch 58 by the load of the vehicle. Rightward pivotingmovement of the pawl 32 will be stopped by the abutment thereof againstthe fixed stop 36.

As the handle 24 approaches its uppermost position, the toothed wheel $8and the housing 22, as well as the pawl 32, will have rotated downwardlysuch that the projection 34 of the holding pawl 32 is adjacent the nextlower slot 35 of the rack bar 18. The next initial downward motion ofthe handle 24 causes the spring 60 to act as a driving link, i.e., assoon as the handle 24 starts downwardly and the driving pawl 52 startsmov ing leftwardly, the entire spring 60 moves leftwardly, causing thestraight spring end section 88 to once again urge the projection 34 ofthe holding pawl 32 into the next adjacent lower slot 35 of the rack bar18. .This, of course, transfers the load from the driving pawl 52 to theholding pawl 32, ready for the next transfer of the projection 56 of thepawl 52 to the next left slot 58 of the wheel 41%.

It should be apparent that there is virtually no lost motion of thehandle 245 between successive strokes thereof, either at the top orbottom portions of each stroke by virtue of the immediate interplaybetween the projections of the pawls 32 and 52 on the respective notches35 and 58 of the rack bar 18 and the toothed wheel 43, depending uponthe position of the tab 98 of the selector lever 36117 relative to thespring 60.

it should also be realized that, as a result of the leverage advantageof the shaped linkage member 42, the position of the pivot 54 on thelink 42, and the distance between the pivots 25 and 38, substantiallyless manual effort is required on the handle 24, in order to cause thewheel 48 to walk up or down the rack bar 18, than is the case forconventional lift pawl and bandle arrangement. in the latter, the liftpawl is limited with respect to how close its pivot can be locatedrelative to the pivot point of the handle and still have sufficientmetal therebetween to support the load to be lifted by the action of thelift pawl on the rack. Furthermore, the latter arrangement incorporatesa so-called lost motion" movement at the top and bottom of each strokeof the handle, represented generally by curve segments A and B of FIG.13, in order for the respective lift and hold pawls to alternately meshwith and release from the rack bar. The advantage of the applicantsimproved jack is represented generally by the respective downwardly andupwardly extending effort-vs-travel curve segments C and D, FIG. 13, theeffort varying between, say, 45 and 80 pounds, as compared to thesubstantially level approximately 90- pound effort curve B for a typicalprior art jack.

While but one embodiment of the invention has been shown and described,other modifications thereof are possible.

Iclaim:

1. For use with a vehicle, a lifting jack comprising a vertical rackbar, a housing slidably mounted thereon, a lifting member pivotallymounted on said housing for engaging said vehicle during raising andlowering thereof, a handle, a pivot for pivotally mounting said handleon said housing, a holding pawl pivotally mounted on said housing andoperative to engage said rack bar to at times support the weight of saidvehicle, a toothed wheel member in mesh with said rack bar and operativeto rotate upwardly and downwardly thereon to raise and lower saidvehicle, linkage means pivotally mounted on an end portion of saidhandle apart from said pivot and extending to the axis of said toothedwheel member, a driving pawl pivotally connected to said linkage meansand operative to engage said toothed wheel member to cause said wheelmember to rotate to move along said rack bar in response to manualmovement of said handle, spring means operatively connected at therespective ends thereof to said driving and holding pawls, and selectormeans for tensioning said spring means to cause said spring means tourge said driving and holding pawls toward said rack bar and said wheelmember, respectively.

2. For use with a vehicle, a lifting jack comprising a vertical rackbar, a housing slidable therealong, a lifting member pivotally mountedon said housing for engaging said vehicle during raising and loweringthereof, a handle pivotally mounted on said housing, a holding pawlpivotally mounted on said housing and operative to engage said rack barto at times support the weight of said vehicle, a toothed wheel memberin mesh with said rack bar and operative to rotate upwardly anddownwardly thereon to raise and lower said vehicle, linkage meansbetween an end portion of said handle adjacent the pivotal mountingthereof and the axis of said toothed wheel member, a driving pawlpivotally connected to said linkage means and operative to engage saidtoothed wheel member to cause said wheel member to rotate to move alongsaid rack bar in response to manual movement of said handle, springmeans operatively connected at the respective ends thereof to saiddriving and holding pawls, and selector means for tensioning said springmeans to cause said spring means to urge said driving and holding pawlstoward said rack bar and said wheel member, respectively, to raise saidvehicle upon lowering said handle, and for untensioning said springmeans to permit said spring means to urge said driving and holding pawlsaway from said rack bar and said wheel member, respectively, to lowersaid vehicle upon raising said handle.

3. For use with a vehicle, a lifting jack comprising a vertical rackbar, a housing slidable therealong, a lifting member pivotally mountedon said housing for engaging said vehicle during raising and loweringthereof, a handle pivotally mounted on said housing, a holding pawlpivotally mounted on said housing and operative to engage said rack barto at times support the weight of said vehicle, a toothed wheel memberin mesh with said rack bar and operative to rotate upwardly anddownwardly thereon to raise and lower said vehicle, a first straightlinkage member pivotally connected at one end thereof to an end portionof said handle, a second linkage member having an intermediate bendportion formed thereon pivotally connected between the other end of saidfirst linkage member and the axis of said toothed wheel member, adriving pawl pivotally connected to said second linkage member andoperative to engage said toothed wheel member to cause said wheel memberto rotate to move along said rack bar in response to manual movement ofsaid handle, a contoured spring member operatively connected at therespective ends thereof to said driving and holding pawls, and selectormeans for alternately tensioning and untensioning said spring member tocause said spring member to alternately urge said driving and holdingpawls toward and away from said rack bar and said wheel member,respectively.

4. For use with a vehicle, a lifting jack comprising a vertical rackbar, a housing slidable therealon g, a lifting member pivotally mountedon said housing for engaging said vehicle during raising and loweringthereof, a handle pivotally mounted on said housing, a holding pawlpivotally mounted on said housing and operative to engage said rack barto at times support the weight of said vehicle, a toothed wheel memberin mesh with said rack bar and operative to rotate upwardly anddownwardly thereon to raise and lower said vehicle, first and secondlinkage members pivotally connected between a pivotable end portion ofsaid handle and the axis of said toothed wheel member, a driving pawlpivotally connected to said second linkage member and operative toengage said toothed wheel member to cause said wheel member to rotate tomove along said rack bar in response to manual movement of said handle,spring means operatively connected at the respective ends thereof tosaid driving and holding pawls, selector means for alternatelytensioning and untensioning said spring means to cause said spring meansto alternately urge said driving and holding pawls toward and away fromsaid rack bar and said wheel member, respectively, and a fixed abutmentmember for at times directing said driving pawl into mesh with saidwheel member.

5. A lifting jack comprising a base, a vertically disposed rack barhaving teeth and intermittent notches formed therealong and mounted insaid base, a housing slidable along said rack bar, a handle pivotallyconnected to said housing, a lifting member pivotally connected to saidhousing, a holding pawl pivotally connected to said housing and operableto engage said notches of said rack bar, a wheel having teeth andintermittent notches formed around the outer periphery thereof, saidteeth meshing with said notches of said rack bar below said holdingpawl, a first linkage member pivotally mounted on said handle apart fromthe pivotal connection of said handle on said housing, a second linkagemember pivotally interconnecting said wheel and said first linkagemember, a driving pawl pivotally connected to an intermediate point ofsaid second linkage member and operable to engage said notches of saidwheel, a contoured spring resiliently interconnecting said driving andholding pawls, a selector tab for alternate engagement and disengagementwith an intermediate point of said contoured spring, and first andsecond fixed abutments for at times being contacted by said driving andholding pawls, respectively.

6. The lifting jack described in claim 5, wherein said first linkagemember is straight and said second linkage member includes a bendportion intermediate the ends thereof, with said driving pawl beingpivotally mounted at said bend portion.

7. For use with a vehicle, a lifting jack comprising a base, avertically disposed rack bar having teeth and intermittent notchesformed therealong and mounted in said base, a housing slidable alongsaid rack bar, a handle pivotally connected to said housing, a liftingmember pivotally connected to said housing, a holding pawl pivotallyconnected to said housing and operable to engage said notches of saidrack bar, a wheel having teeth and intermittent notches formed aroundthe outer periphery thereof, said teeth on said wheel meshing with saidnotches of said rack bar below said holding pawl, a straight linkagemember pivotally mounted on said handle apart from the pivotalconnection of said handle on said housing, a bent linkage memberpivotally interconnecting said wheel and said straight linkage member, adriving pawl pivotally connected to an intermediate portion of said bentlinkage member and operable to engage said notches of said wheel, acontoured spring resiliently interconnecting said driving and holdingpawls, a selector tab movable into engagernent with an intermediateportion of said contoured spring for urging said holding pawl intoengagement with the adjacent notch of said rack bar and for urging saiddriving pawl into engagement with the adjacent notch of said wheel, andmovable out of engagement with said contoured spring, means freeing saidspring to urge said holding and driving pawls away from said teeth ofsaid rack bar and wheel, respectively, and a fixed tab for urging saiddriving pawl into engagement with said adjacent tooth of said wheelwhile said selector tab is out of engagement with said spring upondownward movement of said handle, said downward movement of said handlesimultaneously moving said spring to move said holding pawl back intoengagement with said rack bar while said spring selector tab is out ofengagement with said sp ring.

1. For use with a vehicle, a lifting jack comprising a vertical rack bar, a housing slidably mounted thereon, a lifting member pivotally mounted on said housing fOr engaging said vehicle during raising and lowering thereof, a handle, a pivot for pivotally mounting said handle on said housing, a holding pawl pivotally mounted on said housing and operative to engage said rack bar to at times support the weight of said vehicle, a toothed wheel member in mesh with said rack bar and operative to rotate upwardly and downwardly thereon to raise and lower said vehicle, linkage means pivotally mounted on an end portion of said handle apart from said pivot and extending to the axis of said toothed wheel member, a driving pawl pivotally connected to said linkage means and operative to engage said toothed wheel member to cause said wheel member to rotate to move along said rack bar in response to manual movement of said handle, spring means operatively connected at the respective ends thereof to said driving and holding pawls, and selector means for tensioning said spring means to cause said spring means to urge said driving and holding pawls toward said rack bar and said wheel member, respectively.
 2. For use with a vehicle, a lifting jack comprising a vertical rack bar, a housing slidable therealong, a lifting member pivotally mounted on said housing for engaging said vehicle during raising and lowering thereof, a handle pivotally mounted on said housing, a holding pawl pivotally mounted on said housing and operative to engage said rack bar to at times support the weight of said vehicle, a toothed wheel member in mesh with said rack bar and operative to rotate upwardly and downwardly thereon to raise and lower said vehicle, linkage means between an end portion of said handle adjacent the pivotal mounting thereof and the axis of said toothed wheel member, a driving pawl pivotally connected to said linkage means and operative to engage said toothed wheel member to cause said wheel member to rotate to move along said rack bar in response to manual movement of said handle, spring means operatively connected at the respective ends thereof to said driving and holding pawls, and selector means for tensioning said spring means to cause said spring means to urge said driving and holding pawls toward said rack bar and said wheel member, respectively, to raise said vehicle upon lowering said handle, and for untensioning said spring means to permit said spring means to urge said driving and holding pawls away from said rack bar and said wheel member, respectively, to lower said vehicle upon raising said handle.
 3. For use with a vehicle, a lifting jack comprising a vertical rack bar, a housing slidable therealong, a lifting member pivotally mounted on said housing for engaging said vehicle during raising and lowering thereof, a handle pivotally mounted on said housing, a holding pawl pivotally mounted on said housing and operative to engage said rack bar to at times support the weight of said vehicle, a toothed wheel member in mesh with said rack bar and operative to rotate upwardly and downwardly thereon to raise and lower said vehicle, a first straight linkage member pivotally connected at one end thereof to an end portion of said handle, a second linkage member having an intermediate bend portion formed thereon pivotally connected between the other end of said first linkage member and the axis of said toothed wheel member, a driving pawl pivotally connected to said second linkage member and operative to engage said toothed wheel member to cause said wheel member to rotate to move along said rack bar in response to manual movement of said handle, a contoured spring member operatively connected at the respective ends thereof to said driving and holding pawls, and selector means for alternately tensioning and untensioning said spring member to cause said spring member to alternately urge said driving and holding pawls toward and away from said rack bar and said wheel member, respectively.
 4. For use with a vehicle, a lifting jack comprising a vertical rack bar, a housing slidable therealong, a lifting member pivotally mounted on said housing for Engaging said vehicle during raising and lowering thereof, a handle pivotally mounted on said housing, a holding pawl pivotally mounted on said housing and operative to engage said rack bar to at times support the weight of said vehicle, a toothed wheel member in mesh with said rack bar and operative to rotate upwardly and downwardly thereon to raise and lower said vehicle, first and second linkage members pivotally connected between a pivotable end portion of said handle and the axis of said toothed wheel member, a driving pawl pivotally connected to said second linkage member and operative to engage said toothed wheel member to cause said wheel member to rotate to move along said rack bar in response to manual movement of said handle, spring means operatively connected at the respective ends thereof to said driving and holding pawls, selector means for alternately tensioning and untensioning said spring means to cause said spring means to alternately urge said driving and holding pawls toward and away from said rack bar and said wheel member, respectively, and a fixed abutment member for at times directing said driving pawl into mesh with said wheel member.
 5. A lifting jack comprising a base, a vertically disposed rack bar having teeth and intermittent notches formed therealong and mounted in said base, a housing slidable along said rack bar, a handle pivotally connected to said housing, a lifting member pivotally connected to said housing, a holding pawl pivotally connected to said housing and operable to engage said notches of said rack bar, a wheel having teeth and intermittent notches formed around the outer periphery thereof, said teeth meshing with said notches of said rack bar below said holding pawl, a first linkage member pivotally mounted on said handle apart from the pivotal connection of said handle on said housing, a second linkage member pivotally interconnecting said wheel and said first linkage member, a driving pawl pivotally connected to an intermediate point of said second linkage member and operable to engage said notches of said wheel, a contoured spring resiliently interconnecting said driving and holding pawls, a selector tab for alternate engagement and disengagement with an intermediate point of said contoured spring, and first and second fixed abutments for at times being contacted by said driving and holding pawls, respectively.
 6. The lifting jack described in claim 5, wherein said first linkage member is straight and said second linkage member includes a bend portion intermediate the ends thereof, with said driving pawl being pivotally mounted at said bend portion.
 7. For use with a vehicle, a lifting jack comprising a base, a vertically disposed rack bar having teeth and intermittent notches formed therealong and mounted in said base, a housing slidable along said rack bar, a handle pivotally connected to said housing, a lifting member pivotally connected to said housing, a holding pawl pivotally connected to said housing and operable to engage said notches of said rack bar, a wheel having teeth and intermittent notches formed around the outer periphery thereof, said teeth on said wheel meshing with said notches of said rack bar below said holding pawl, a straight linkage member pivotally mounted on said handle apart from the pivotal connection of said handle on said housing, a bent linkage member pivotally interconnecting said wheel and said straight linkage member, a driving pawl pivotally connected to an intermediate portion of said bent linkage member and operable to engage said notches of said wheel, a contoured spring resiliently interconnecting said driving and holding pawls, a selector tab movable into engagement with an intermediate portion of said contoured spring for urging said holding pawl into engagement with the adjacent notch of said rack bar and for urging said driving pawl into engagement with the adjacent notch of said wheel, and movable out of engagement with said contoured spring, means freeing said spring to urgE said holding and driving pawls away from said teeth of said rack bar and wheel, respectively, and a fixed tab for urging said driving pawl into engagement with said adjacent tooth of said wheel while said selector tab is out of engagement with said spring upon downward movement of said handle, said downward movement of said handle simultaneously moving said spring to move said holding pawl back into engagement with said rack bar while said spring selector tab is out of engagement with said spring. 